The invention relates to a lengthwise adjustable wishbone for sailboards, with two main spars connected by a wishbone head section and with two extension spars adjustable in these main spars telescopically, these extension spars being joined on the stern line side by means of an elastic wishbone end section, as well as to devices for locking the spars, with the length of the wishbone being set in correspondence with the size of the sail, by means of respectively one inner sleeve fixedly connected to the ends of the main spars, such sleeve exhibiting locking tongues projecting beyond the end of the main spar in the axial direction with radially outwardly protruding clamping parts wherein radially inwardly protruding locking ring segments are formed at the ends of the locking tongues, these segments extending in the peripheral direction, and with an outer sleeve fashioned as a clamping sleeve, which can be locked with the inner sleeve, this outer sleeve, when pushed onto the inner sleeve, compressing the locking tongues arranged at the latter so that the locking ring segments formed at the locking tongues lock into peripheral grooves arranged at spacings on the extension spars.
In a lengthwise adjustable wishbone-shaped boom of this type, known from EP 0317661 Al, the outer sleeves equipped with an internal thread are threaded on the inner sleeves exhibiting a corresponding outer thread in order to lock the main spars to the extension spars. The trapezoidal seats primarily employed at present in sailboards bring about a strong torsional stress on the wishbone so that there is the danger that the meshing threads of the inner and outer sleeves will seize when the wishbone of this type is locked in place and consequently the locking engagement can be released only with great expenditures of force and frequently only with the aid of tools. Furthermore, the conventional locking mechanism is relatively expensive and cumbersome in handling.
The invention is based on the object of further developing the wishbone of this type with a view toward higher functional safety and simpler manipulation of the locking mechanism.